To solve this problem, downloaders stop seeding, which causes there to be fewer seeders for the torrent.

There are many torrents of large collections that are dead.  If the videos had been in individual torrents, it is likely that at least some of them would still be alive.

The more videos in the collection and the less well-defined the theme, the more likely it is that someone will only partially download the torrent.

i am seeding a number of torrents where i didnt download everything,  eg  i downloaded 10gb or a 20gb torrent.  Becasue i have a number of these,  it says i am still leeching these when in fact i have finished downloading what i want,  so it then affects my concurrent downloads and i get   too many downloads bad ratio,  is there a way to make the partially downloaded (completed) torrents  set as completed,  without  having to stop seeding them?

thanks

Unfortunately, this can happen, and I don't think there is very much you can do about it. Sometimes people do a partial download, ultimately sometimes effecting other people's ratio. Perhaps the owner can think about adding a feature in the bonus point section, to buy out all that is perceived "hit and runs." Or just use your current points to fix your ratio. That's what it's  there for.